In a lawn mower with a floating cutting platform, the mowing height is adjusted by adjusting the elevation of the cutting platform relative to the chassis. The floating cutting platform is one of the most common applied mechanisms in lawn mowers. The structure of the cutting platform is: an engine is fixed to the chassis, and the engine transfers power to the belt pulley on the cutting platform via the belt pulley fixed to the engine and the drive belts on the cutting platform. Since the elevation of the cutting platform relative to the chassis is adjustable, the elevation of the belt pulley fixed to the cutting platform is variable accordingly, in relation to the belt pulley fixed to the engine. As a result, the drive belts that connect the two belt pulleys are often oblique. Oblique belts will enhance belt abrasion and greatly shortened belt service lifespan.
In order to overcome above technical drawbacks, in some current lawn mowers, the belt inclination is reduced by reducing the adjusting range of the cutting platform, so as to increase belt service lifespan. However, the applicability of the integral unit will be reduced due to the range reduction of mowing height. In some lawn mowers, two belt pulleys are designed below the engine, wherein, the upper belt pulley matches higher elevation of the cutting platform, while the lower belt pulley matches lower elevation of the cutting platform, so as to attain the object of reducing belt inclination. However, a lawn mower with such a mechanism is difficult to operate, and hard to remember the belt pulley switching operation. Once the operator forgets to switch the belt pulley, the belt will be more oblique, and the belt service lifespan will be shortened even more.